Remove includeconf nested scope

Summary:
Easier to review ignoring whitespace

Suggestion from John Newbery <john@johnnewbery.com> in
https://github.com/bitcoin/bitcoin/pull/15934#discussion_r343806860

This is a partial backport of Core PR15934 : https://github.com/bitcoin/bitcoin/pull/15934/commits/e2e37cfe8af088bd8ea884be2f79f0f3cac555d5

Test Plan:

ninja all check

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D5905